1. Field of the Invention
The present invention relates to a light emitting diode with an improved protection function for electrostatic discharge impact. More particularly, the present invention relates to a light emitting diode that has a current leakage passage electrically connected in parallel to an active layer to protect the light emitting diode from the static electricity and to provide better reliability in anti-electrostatic performance.
2. Discussion of the Background
Light emitting diodes (LEDs) are devices that convert an electric current into light when the current is input forward into an active layer of the devices. For emitting infrared rays, red light, and the like, the LED is formed of chemical compounds such as InP, GaAs, GaP, and the like. Further, a GaN-based semiconductor has been developed as a material for an LED for emitting ultraviolet rays, blue light, or green light.
To prevent generation of crystal defects, the GaN-based semiconductor is generally grown by an epitaxy process on a sapphire substrate, which has similar crystal structure and lattice constant as those of the semiconductor. Since sapphire is an insulator, electrode pads for the LED are formed on a grown surface of an epitaxial layer. However, for a substrate made of an insulator such as sapphire, it is difficult to prevent electrostatic discharge (ESD) caused by static electricity injected from the outside. As a result, the LED may be damaged by the electrostatic discharge, which reduces reliability of the LED. Thus, when packaging the LED, a separate Zenor diode is mounted along with the LED to prevent ESD.
FIG. 1A is a schematic cross-sectional view of a flip-chip LED with a Zenor diode on a sub-mount to prevent ESD damage, and FIG. 1B is an equivalent circuit diagram of the flip-chip LED shown in FIG. 1A. Referring to FIG. 1A, a semiconductor light emitting device includes an LED 125 and a Zenor diode 155, which is connected in parallel to the LED 125 and formed on a sub-mount 151. The LED 125 includes an n-type semiconductor layer (for example, n-GaN) 103 on a sapphire substrate 101, an active layer 105 on the n-type semiconductor layer 103, a p-type semiconductor layer (for example, p-GaN) 107 on the active layer 105, an n-electrode 111 on the n-type semiconductor layer 103, and a p-electrode 109 on the p-type semiconductor layer 107. The Zenor diode 155 can be formed by injecting, for example, p-type ions into a portion of the sub-mount 151 such as an n-type silicon substrate to form a p-type silicon region 153. In the LED 125, the n-electrode 111 is connected to the p-type silicon region 153 via a first conductive bump 113, and the p-electrode 109 is connected to the sub-mount 151 such as the n-type silicon substrate via a second conductive bump 115, followed by flip chip bonding. If ESD voltage is applied through input/output terminals (not shown) of the semiconductor light emitting device shown in FIG. 1A, most discharge current flows through the Zenor diode 155 connected in parallel to the LED 125, as also shown in FIG. 1B. With this configuration, the LED 125 can be protected from inadvertent application of the ESD voltage.
For the light emitting device shown in FIG. 1A, formation of the Zenor diode 155 on the sub-mount 151 requires an expensive ion-injection process and a diffusion process that is difficult to control, thereby leading to a complex process and an increased cost in manufacturing the sub-mount 151.
For not only the flip chip LED described above but also general surface emission LEDs, using the Zenor diode increases the number of processes and manufacturing costs for packaging the LED along with the Zenor diode, and makes it more difficult to arrange the LED and the Zenor diode in the package.